1. Field of the Invention
The present invention relates to a printer in which a platen roller and a recording head are separably combined with each other.
2. Description of the Related Art
In recent years, a number of various kinds of thermal printers have been provided, which perform printing by pressing a thermal head against a special recording sheet that develops color when applying heat to the recording sheet. In particular, the thermal printers enable smooth character printing and colorful graphic printing without using toner, ink, etc., and hence the thermal printers are used preferably for printing of various labels, sales checks, tickets, and the like.
In general, a recording sheet to be used in various kinds of printers typified by the thermal printers is fed to a downstream side through rotation of a platen roller while being sandwiched between a recording head and the platen roller.
At this time, normally, the recording sheet is smoothly pulled apart from the platen roller to be fed to the downstream side. However, according to circumstances, the recording sheet may not be pulled apart from the platen roller, and may be rotated together with the platen roller so as to be caught around the platen roller, in other words, so-called paper jam may occur. In addition, once the paper jam occurs, the recording sheet is caught in succession along with the rotation of the platen roller, which finally causes the recording sheet to be caught around the platen roller.
When such paper jam occurs, printing is stopped halfway, and hence quick recovery is important.
Incidentally, in order to increase workability when setting the recording sheet and when maintaining or replacing the recording head, the platen roller, and the like, there are conventionally known separation-type printers which include a main unit and a detachable unit separably combined with each other, and in which a recording head is provided to one of the units and a platen roller is provided to the other of the units.
Among the separation-type printers, when paper jam occurs in a printer of a type in which the platen roller is provided to the detachable unit, by separating the detachable unit from the main unit, the platen roller is exposed, and a drive system for driving the platen roller is separated from the main unit to be in a free state. Therefore, it is possible to rotate the platen roller freely, and it is relatively easy to perform removal of the recording sheet caught around the platen roller. Therefore, it is easy to quickly perform an operation for recovery from paper jam.
In contrast, when paper jam occurs in a printer of a type in which the platen roller is provided to the main unit, by separating the detachable unit from the main unit, the platen roller can be exposed. However, the drive system for driving the platen roller remains connected to a motor. With this configuration, due to an influence of holding torque or the like of the motor, the platen roller remains applied with load.
Therefore, it is difficult to rotate the platen roller freely, and hence it requires time and effort to remove the recording sheet caught around the platen roller.
In particular, it is impossible to control a caught amount of the recording sheet, and hence a large amount of the recording sheet is caught around the platen roller in the case of long printing distance. As a result, the recording sheet is caught around the platen roller in multiple layers in many cases. In such cases, removal of the recording sheet is particularly difficult. In addition, there is a high risk that the recording sheet is torn halfway through removing of the recording sheet, which frequently makes the removal more difficult.
In this context, there is known a recording device capable of quickly detecting paper jam to stop a motor for feeding a recording sheet (see Japanese Patent No. 3276778).
The recording device includes a paper feed sensor for detecting the recording sheet fed from a paper feed portion, a paper delivery sensor for detecting the recording sheet delivered to a paper delivery portion, and detection means for detecting paper jam of the recording sheet based on detection results of both the sensors. According to the recording device, the paper jam can be detected early with use of the sensors, and hence it is possible to prevent the recording sheet from being excessively caught around the platen roller.
Therefore, even in the printer of the type in which the platen roller is provided to the main unit, it is possible to suppress the paper jam, and to easily perform quick removal of the recording sheet.
However, in the case of adopting a mechanism for detecting the paper jam with use of sensors into the separation-type printer, it is necessary to control signals related to various kinds of sensors. Thus, the control and the configuration are complicated, and the parts count is increased, which leads to an increase in cost.
In particular, when inconvenience such as breakdown or malfunction of the sensors occurs, it is impossible to detect the paper jam early. As a result, the paper jam proceeds so that a large amount of the recording sheet is caught, and hence there is a fear that the recording sheet is caught in multiple layers.